The UREX process was tested in miniature centrifugal contactors during 2003 as part of a series of five different solvent extraction processes called

UREX+ (Vandegrift 2004). A fuel pin with an estimated burn-up of 29,600 MWd/MT, 4.6% initial 235U enrichment, and a cooling time of 21 years was dissolved and used as feed in this process test. After dissolution, the first solvent extraction step was the UREX process where U and Tc were separated from the other actinides and fission products. The process used AHA in the scrub section of the flowsheet to remove neptunium and plutonium from the organic phase (Fig. 6.5), and route these actinides to

the raffinate end of the cascade. In order for the AHA to complex the tetravalent actinides, the acidity of the feed solution was adjusted to a fairly low acidity of ~1 M HNO3, which also resulted in increased technetium extraction. A separate technetium strip contactor using higher acid concen­tration was included in the UREX process (Fig. 6.5). To remove excess nitric acid, an acid scrub contactor was included after the Tc strip, but before the final uranium strip. The uranium product obtained from this process test reached the limits for FP decontamination. But due to a mechanical failure during processing, the desired TRU decontamination was unsuccessful. The indications were positive and a second test was carried out one year later. Tc recovery was 95% which was in line with the requirements set on the process. Recycling of the spent solvent was not carried out during the test, but solvent degradation is fairly well established as discussed above, and would likely not be affected by the addition of AHA to the process. As previously mentioned, hydroxamic acid has low solubility in the organic solvent and a solvent clean up stage would remove any residual AHA along with any dissolved HNO3.